How to fix a mutation permanently in a population was proposed in theory by J.B.S. Haldane 90 years ago. Theory never was supported by experimental data. Now data is present and theory isn't working as thought:-http://medicalxpress.com/news/2013-09-fate-genes.html -"By performing competition tests in roundworms, they have confirmed this theory for the introduction of a new beneficial allele in a population. However, the researchers found that this theory cannot predict the ultimate fate of the allele. This study, published in the latest issue of the scientific journal Nature Communications, contributes to a better comprehension of how a population can evolve, with implications for studies on how species adapt to changing environments or species conservation."-It works early but not later on.